There is no way to know if a vaccine works for a period of time if you don't wait for that period of time to see the results.I am under the impression that there are a number of vaccines that "work" currently in safety trials.
Russia and China had a vaccine that may or may not "work" that was released months ago.
China gave it to soldiers in the army and Russia released it to the general public.
Of course with both countries they cannot be relied on to be truthful about anything that could reflect poorly on either country.
That is why it takes years to know. Giving vaccines to large amounts of people means nothing until the results are in
years down the road.